1. Field of the Invention
The present invention relates to a roller for feeding or transporting sheets, such as originals or recording paper, to an image forming apparatus, such as a copying machine, a printer, or a facsimile apparatus. The present invention also relates to a sheet feed apparatus and an image forming apparatus using this roller.
2. Related Background Art
In a sheet feed apparatus for feeding sheets, such as recording paper or originals, it is necessary to supply contained sheets one by one. For this purpose, there is available, for example, a retard separation type sheet feed apparatus 201 shown in FIG. 11 for feeding sheets one by one.
The sheet feed apparatus 201 shown in FIG. 11 is equipped with a pick-up roller 205 for feeding a plurality of sheets from a sheet containing device 203, in which a plurality of sheets are stacked on a stack table (not shown), one by one starting with the uppermost sheet 202, a feed roller 206 for feeding the sheet 202, fed from the sheet containing device 203 by the pick-up roller 205, into an image forming apparatus main body (in the direction indicated by the arrow xe2x80x9cbxe2x80x9d in the FIG. 11), a retard roller 207 which is opposed to the feed roller 206 and which, when a plurality of sheets are fed from the sheet containing device 203, rotates in a rotating direction reverse to the rotating direction for feeding sheets to thereby separate the plurality of sheets into a single sheet 202, and a transport roller pair 209 for transporting the separated sheet.
Further, in a sheet passage region 210 between the pick-up roller 205 and the roller set consisting of the feed roller 206 and the retard roller 207, there is arranged a guide 211. Between the roller set consisting of the feed roller 206 and the retard roller 207 and the transport roller pair 209, and between the transport roller pair 209 and the image forming apparatus main body, there are arranged guides 212, each guiding the sheet 202.
A drive transmission device 213 shown in FIG. 12 drives the feed roller 206 and the retard roller 207.
As shown in FIG. 12, in the drive transmission device 213, a feed roller shaft 215 supporting the feed roller 206, a retard roller shaft 216 supporting the retard roller 207, and a retard roller driving shaft 217 connected to the retard roller shaft 216, are arranged substantially parallel to each other. The retard roller shaft 216 is supported by an oscillatable support member (not shown) and capable of moving toward and away from the feed roller shaft 215 so as to be parallel to the same. Further, between the retard roller shaft 216 and the retard roller driving shaft 217, there are arranged a coupling 219 and a torque limiter 220. Further, at an end portion of the feed roller shaft 215, there is provided an electromagnetic clutch 222 for transmitting the driving force transmitted from a main driving unit of the image forming apparatus main body (not shown) to the feed roller shaft 215 through a drive input belt 221. Further, wrapped around the feed roller shaft 215 and the retard roller driving shaft 217 is a retard driving belt 223 for transmitting to the retard roller driving shaft 217 a rotational driving force transmitted to the feed roller shaft 215. Note that the coupling 219 serves to transmit a driving force from the retard roller driving shaft 217 to the retard roller shaft 216 even when the retard roller 207 is displaced.
The driving of the feed roller 206 and the retard roller 207 by the drive transmission device 213 will be described. The rotational driving force supplied from the main driving unit of the image forming apparatus main body (not shown) is transmitted to the drive input belt 221, and input to a pulley 225 provided on the armature portion of the electromagnetic clutch 222 ON/OFF-controlled in accordance with the sheet feed timing. Here, the feed roller shaft 215 rotating integrally with the rotor portion of the electromagnetic clutch 222 is connected to the retard roller driving shaft 217 and the retard roller shaft 216 by the retard driving belt 223, so that the feed roller shaft 215, the retard roller shaft 216, and the retard roller driving shaft 217 rotate in the same direction, and the feed roller 206 and the retard roller 207 are driven to be rotated in synchronism with each other when the sheet feed timing is ON.
When the sheets 202 are fed one by one in the sheet feeding direction (the direction indicated by the arrow xe2x80x9cbxe2x80x9d in FIGS. 11 and 12) by the rollers rotated by the driving force transmitted by the drive transmission unit 213, the torque limiter 220 makes idle rotation due to the frictional force between the feed roller 206 and the sheet 202, and the retard roller 207 rotates in the direction reverse to the direction in which the retard roller driving shaft 217 is driven to be rotated.
When a plurality of sheets 202 are fed, the torque limiter 220 makes no idle rotation due to the fact that the frictional force between the plurality of sheets 202 is smaller than the frictional force between the retard roller 207 and the sheets 202, and the retard roller 207 rotates in the same direction as the retard roller driving shaft 217. As a result, the sheet 202 nearest to the feed roller 206 side, that is, the uppermost sheet 202, is separated from the rest of the plurality of sheets 202, thereby preventing double feed of sheets 202 into the image forming apparatus main body. Note that, in the following, the phenomenon in which a plurality of sheets are fed from the sheet containing device to the retard roller will be referred to as xe2x80x9cstack transportxe2x80x9d, and the phenomenon in which a plurality of sheets are allowed to be fed into the image forming apparatus main body without being separated by the retard roller will be referred to as xe2x80x9cdouble feedxe2x80x9d.
Next, theoretical formulas satisfying the conditions for the feeding and separation of the sheets 202 by the sheet feed apparatus 201, constructed as described above, will be illustrated.
N greater than T/rxcexcBP+(xcexcAPPxcexcAP)W/xcexcBPxe2x80x83xe2x80x83(1)
N less than T/rxcexcBPP2xcexcAPPW/xcexcBPPxe2x80x83xe2x80x83(2)
N less than T/rxcexcCPxe2x80x83xe2x80x83(3)
where
xcexcAP: the coefficient of friction between the pick-up roller 205 and the sheets 202;
xcexcBP: the coefficient of friction between the feed roller 206 and the sheets 202;
xcexcCP: the coefficient of friction between the retard roller 207 and the sheets 202;
xcexcAPP: the coefficient of friction between the sheets 202 under the pressure portion of the pick-up roller 205;
xcexcBPP: the coefficient of friction between the sheets 202 at the nip portion of the feed roller 206 and the retard roller 207;
N: the pressure force of the retard roller 207;
T: the idle torque of the torque limiter 220;
r: the radius of the retard roller 207; and
W: the pressure force of the pick-up roller 205.
Formula (1) satisfies the feeding condition, formula (2) satisfies the separating condition, and formula (3) satisfies the retard roller associative rotation condition.
Note that, if the sheets used in the above formulas are the same, there is no great variation in coefficient of friction between the roller pressure portions, so that through the substitution: xcexcAPP≈xcexcBPP=xcexcPP, the following formulas (4) and (5) are obtained from formulas (1) and (2):
N  greater than T/rxcexcBP+(xcexcPPxe2x88x92xcexcAP)W/xcexcBPxe2x80x83xe2x80x83(4)
N less than T/rxcexcPPxe2x88x922Wxe2x80x83xe2x80x83(5)
FIG. 13 is a graph showing the relationship between the above formulas (3), (4) and (5), using the pressure force N of the retard roller 207 and the idle torque T of the torque limiter 220 as parameters.
In FIG. 13, the shaded portion indicates the feed region.
Thus, to enlarge the shaded region, it is necessary either to increase the coefficient of friction between the rollers and sheets or to reduce the pressure force of the pick-up roller 205. Further, it can be understood that the feed region is enlarged by setting the feeding condition such that both the pressure force N of the retard roller 207 and the idle torque T of the torque limiter 220 increase (upper right in FIG. 13).
JP 07-117880 A proposes a novel technique for enlarging the feed region, which helps to markedly improve the separation performance for the sheets stack-transported from the sheet containing device. According to this revolutionary technique, the retard roller is formed of a resilient material like sponge, and the nip configuration of the press-contact portion between the feed roller and the retard roller is concave toward the retard roller side, whereby it is possible to achieve the following three advantages, which are not to be attained with the conventional retard roller of synthetic rubber.
(1) An improvement in stack sheet separation ability is achieved due to the enlargement of the nip width.
(2) By forming the roller of a resilient material, the chattering noise from the roller and fluttering of the separated sheet during separating operation are eliminated.
(3) Due to the reduction in the requisite torque for the torque limiter, the roller service life is elongated, and skew feed is mitigated.
However, even a retard roller formed of a resilient material like sponge, which is ideal as far as the separation performance is concerned, involves the following problems.
Due to its characteristics, a sponge material is never free from permanent set. Thus, if the retard roller, which is constantly in press contact with the feed roller, is left as it is for a long period of time, in particular, in a high-temperature/high-humidity environment, it becomes rather difficult for the concave nip portion to be restored to the original substantially round configuration. Then, the concave-portion-radius of the retard roller as compared with that in the other phase is reduced, with the result that the stack sheet return force in the roller-periphery-tangential direction increases. While this is a phenomenon advantageous from the viewpoint of stack sheet separation, it involves an increase in the associative rotation resistance of the retard roller when the sheets are fed one by one, so that damage to the feed roller is accumulated, causing feed slip (feed jam) to occur frequently. Further, in the above-mentioned conventional technique, coating is effected on the outer peripheral surface of the sponge base material to thereby maintain the requisite strength of the surface layer, which means the roller in itself is rather expensive as compared with one formed of synthetic rubber.
In view of the above problems, JP 06-329282 A, JP 06-340343 A, JP 10-316257 A, etc. disclose techniques according to which a hollow retard roller of synthetic rubber is used and of which the same effect as that of the retard roller of sponge is to be expected. However, in these techniques, a roller side wall supporting the roller outer peripheral portion in contact with the sheet is present on either side, so that the nip configuration in the roller press-contact portion is flat, which means it is rather difficult to realize a concave configuration in conformity with the outer peripheral surface of the feed roller.
In view of the above problems in the conventional art, it is an object of the present invention to provide a sheet feed apparatus which adopts an inexpensive roller construction in which the permanent set in the roller press-contact portion is mitigated, making it possible to maintain for a long period of time the stack sheet separation performance as obtained with a resilient retard roller formed of a sponge material or the like.
According to the present invention, there is provided a roller including:
an outer peripheral portion coming into contact with a sheet;
an inner peripheral portion; and
a plurality of connection ribs for connecting the outer peripheral portion and the inner peripheral portion to each other,
in which the outer peripheral portion and the inner peripheral portion have a cylindrical configuration and are arranged concentrically, and
in which the connection ribs are inclined by a predetermined angle with respect to a straight line radially extending from an axis of the roller.
According to the present invention, there is provided a sheet feed apparatus including:
sheet containing means for containing and supporting sheets;
sheet feeding means for feeding sheets from the sheet containing means; and
a retard separation mechanism for feeding the sheets from the sheet feeding means separately one by one,
in which the retard separation mechanism has a feed roller rotating in the direction in which the sheets are fed and a retard roller in press contact with the feed roller and rotating in the direction in which the sheets are returned to the sheet containing means, and
in which the retard roller has an outer peripheral portion coming into contact with the sheets, an inner peripheral portion, and a plurality of connection ribs for connecting the outer peripheral portion and the inner peripheral portion to each other, the outer peripheral portion and the inner peripheral portion being of a cylindrical configuration and arranged concentrically, the connection ribs being inclined by a predetermined angle with respect to a straight line extending radially from the axis of the retard roller.